Synchronous digital communication systems arrange data into frames according to a predetermined format defined by standard protocols, such as SONET and synchronous digital hierarchy (SDH). Data can be transmitted over a path that includes multiple segments, or “tandem paths”, with each tandem path being managed by a different network operator. The beginning point and termination point of the tandem path are referred to as the source and the sink, respectively. If an error or other fault occurs in the path, the tandem path causing the fault needs to be identified so that the appropriate network operator can take the required action. TCM provides a means for a network operator to quickly determine whether the fault is present in its network or whether the fault exists within a tandem connection managed by a different network operator.
TCM data are carried in a byte in the path overhead (POH) portion of the data frame. Because the position of the POH can vary for different data frames, a pointer processor is required to find the TCM data. The International Telecommunication Union (ITU) standard G.707, option 2 specifies one implementation of TCM in which the TCM sink is present in the egress portion of the network element. The pointer processor enables sink functionality on egress by identifying the TCM data and the appropriate return data are provided to the TCM source on ingress for the reverse path. The addition of a pointer processor requires additional circuit elements (e.g., gates) and increased area in the network element, resulting in higher costs.
Accordingly, there exists a need for a digital communication system that can provide TCM sink functionality on egress without the use of an egress pointer processor. The present invention satisfies this need and provides additional advantages.